Vacuum chamber arrangement for charged particle beam generator

ABSTRACT

The invention relates to charged particle beam generator comprising a charged particle source for generating a charged particle beam, a collimator system comprising a collimator structure with a plurality of collimator electrodes for collimating the charged particle beam, a beam source vacuum chamber comprising the charged particle source, and a generator vacuum chamber comprising the collimator structure and the beam source vacuum chamber within a vacuum, wherein the collimator system is positioned outside the beam source vacuum chamber. Each of the beam source vacuum chamber and the generator vacuum chamber may be provided with a vacuum pump.

This application is a continuation in part of U.S. application Ser. No.14/541,233 filed on 14 Nov. 2014, which claims priority to U.S.provisional application No. 61/904,057 filed on 14 Nov. 2013. Thisapplication is also a continuation in part of U.S. application Ser. No.14/400,569 filed on 12 Nov. 2014, which is a national stage entry ofPCT/EP2013/059963 filed on 14 May 2013, which claims priority to U.S.provisional application No. 61/646,839 filed on 14 May 2012. All theseapplications are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to a charged particle beam generator and to atarget processing machine comprising a charged particle beam generator.More specifically, the invention relates to a vacuum chamber arrangementfor use in a charged particle beam generator or in a target processingmachine comprising a charged particle beam generator.

BACKGROUND

In the semiconductor industry, an ever-increasing desire exists tomanufacture smaller structures with high accuracy and reliability.Lithography is a critical part of such manufacturing process. In amask-less lithography system, charged particle beamlets may be used totransfer a pattern onto a target. The beamlets may be individuallycontrollable to obtain the desired pattern.

To be commercially viable, the charged particle lithography systems needto be able to meet challenging demands for substantial wafer throughputand stringent error margins. A higher throughput may be obtained byusing more beamlets, and hence more current.

However, the handling of a greater number of beamlets results in theneed for more control circuitry. The operational control circuitry maycause heating within the lithography system. Furthermore, an increase inthe current results in more charged particles that interact withcomponents in the lithography system. The collisions between chargedparticles and system components inside the lithography system may causesignificant heating of respective components. The resulting heating ofbeam manipulation components may lead to thermal deformations thatreduce the accuracy of the lithography process.

The use of a large number of beamlets further increases the risk ofunacceptable inaccuracy due to inter-particle interactions between thebeamlets (e.g. Coulomb interactions).

The effects of inter-particle interactions may be reduced by shorteningthe path between particle source and target. Path shortening may beachieved by using stronger electric fields for manipulating the chargedparticles, which requires application of larger electric potentialdifferences between various electrodes in the charged particlelithography system.

With higher electric fields strengths, the shape and layout of thecollimator electrodes become more important determinants of theachievable accuracy for the electric field distribution, and hence onthe beam generation and shaping accuracy.

SUMMARY OF THE INVENTION

It would be desirable to provide a charged particle beam generator andtarget processing machine, which allow the use of a great number ofcharged particle beamlets while achieving high beam collimation fieldaccuracy.

It is an object of the invention to provide a charged particle beamgenerator with an improved vacuum chamber arrangement. For this purpose,the invention provides a charged particle beam generator and a targetprocessing machine as described in this specification and claimed in theappended claims.

It will be evident that the presently invented principle may be set intopractice in various manners.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying schematic drawings, in which correspondingreference symbols indicate corresponding parts, and in which:

FIG. 1 schematically shows a perspective view of a charged particlelithography system according to an embodiment;

FIG. 2 presents a frontal view of a vacuum chamber of a charged particlelithography system according to an embodiment;

FIG. 3 shows a schematic side view of a beam generator according to anembodiment;

FIG. 4 shows a perspective view of a collimator electrode stackaccording to an embodiment;

FIG. 5 shows a perspective view of a collimator electrode according toan embodiment;

FIG. 6 shows a schematic cross-sectional side view of a collimatorelectrode stack according to an embodiment.

FIGS. 7a-7d shown cross-sectional top and side views of collimatorelectrodes according to embodiments;

FIG. 8 shows a detailed top view of a beam generator according to anembodiment;

FIGS. 9-11 show perspective views of a beam generator according toanother embodiment;

FIG. 12 shows a cross-sectional side view of a lower portion of a beamgenerator according to an embodiment;

FIG. 13 shows a cross-sectional side view of a support column in acollimator electrode stack according to an embodiment;

FIG. 14 shows a cross-sectional side view of cooling conduits in acollimator electrode stack according to an embodiment;

FIG. 15 shows a support system in a collimator electrode stack accordingto another embodiment;

FIG. 16 schematically shows an exemplary charged particle beam generatoraccording to an embodiment of the invention;

FIG. 17 schematically shows an overview of an exemplary beam generatoraccording to an embodiment of the invention;

FIG. 18 shows an elevated side view of an exemplary beam generatoraccording to an embodiment of the invention;

FIG. 19 shows a first cross-sectional side view of the beam generator ofFIG. 18;

FIG. 20 shows a second cross-sectional side view of the beam generatorof FIG. 18;

FIG. 21 shows an elevated side view of the beam generator of FIG. 18;and

FIG. 22 shows another elevated side view of the beam generator of FIG.18.

The figures are meant for illustrative purposes only, and do not serveas restriction of the scope or the protection as laid down by theclaims.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The following is a description of certain embodiments of the invention,given by way of example only and with reference to the drawings.

FIG. 1 schematically shows a perspective view of a target processingmachine, such as a lithography system 10. Such a lithography system 10is adapted for lithographic processing of a semiconductor target 31(e.g. the creation of structures onto a resist-covered semiconductorsubstrate). The lithography system 10 comprises (at a lower side) avacuum chamber 30 for accommodating a projection column 46, and (at anupper side i.e. positioned above the vacuum chamber 30) a cabinet 12 foraccommodating electronic equipment 22.

The cabinet 12 comprises a closable casing, defined by wall panels andprovided on a front side with an opening 14 for accessing the interiorof the cabinet 12. Two doors 15 are provided for covering the opening14. The walls and doors define a cuboid shape that can be closed in asealing manner to prevent air from entering the cabinet 12. The cabinet12 encloses laterally spaced racks 18 carrying shelves 20 for housingthe electronic equipment 22. On the top side 32, the vacuum chamber 30is provided with a recessed section that comprises an interface wall 35with access ports 36 for letting through conduits/cables 26 emanatingfrom the beam projection column 46 inside the vacuum chamber 30 toelectronic equipment 22 inside of the cabinet 12.

The vacuum chamber 30 is arranged for accommodating the target 31 andthe projection column 46. The vacuum chamber 30 comprises a vacuumcasing 39 (outer layer) that is configured to retain a vacuumenvironment on its inside (typically 10⁻³ bar or lower). Inside thevacuum casing 39, there is provided a support casing 40 (intermediatelayer), and a carrier casing 41 with a carrier frame 42 (innermostregion). The projection column 46 is supported by the carrier frame 42on an inside of the carrier casing 41. The projection column 46 isconfigured for generating and manipulating multiple processing beamlets47 that are used for processing the target 31. The projection column 46may comprise various optical elements. Exemplary elements may be: anaperture array for forming a plurality of beamlets from the chargedparticle beam, a beamlet modulator for patterning the beamlets to formmodulated beamlets, and a beamlet projector for projecting the modulatedbeamlets onto a surface of the target 31.

FIG. 2 shows a simplified schematic drawing of an embodiment of acharged particle lithography system 10. Such lithography systems aredescribed for example in U.S. Pat. Nos. 6,897,458; 6,958,804; 7,019,908;7,084,414; 7,129,502; 8,089,056 and 8,254,484; U.S. patent applicationpublication no. 2007/0064213; 2009/0261267; US 2011/0073782; US2011/0079739 and US 2012/0091358, which are all assigned to the owner ofthe present invention and are all hereby incorporated by reference intheir entirety.

FIG. 2 presents a frontal view a vacuum chamber 30 of a targetprocessing system 10. The projection column 46 with a charged particlebeam generator 50 is accommodated by the carrier frame 42 on the insideof the vacuum chamber 30. The charged particle beam generator 50 isformed as a beam generator module that is insertable into and removablefrom the carrier frame 42 inside the vacuum chamber 30 of the chargedparticle lithography system 10. The carrier casing 41 and carrier frame42 are moveably suspended within the support casing 40 by means ofsuspension members 44 (e.g. leaf springs) that are connected to asuspension base 43, which in turn is moveably interconnected with thecarrier casing 41 by means of a plurality of rigid but laterallyhingeable suspension rods 45.

A charged particle beam 54 is generated by the charged particle beamgenerator 50, and subsequently manipulated by the various opticalelements provided in the projection column 46.

The term “refracting” is used herein to generally indicate the action ofdeflecting portions of a beam. The term “collimating” is used herein toindicate the action of making various portions of a beam more parallel.

FIG. 3 shows a schematic cross-sectional view of a beam generator module50 according to an embodiment. The cross sectional view is defined in anaxial-radial plane i.e. which is spanned by the axial direction Z andthe radial direction R.

Shown in FIG. 3 is a beam generator chamber 51, which encloses elements,components and/or modules that make up the beam generator 50. The beamgenerator 50 comprises a charged particle beam source 52, a collimatorstack 70, and vacuum pumps 122, 123 for creating a vacuum inside thebeam generator chamber 51 (only vacuum pump 122 is shown).

The beam source 52 is accommodated within a beam source vacuum chamber53, which in turn is located within the beam generator chamber 51. Thebeam source 52 is fixed to a top side of the collimator stack 70, andconfigured to generate a charged particle beam 54 along optical axis A.The beam source chamber 53 encloses source vacuum pump units 120, whichallow an ultra-low vacuum to be created locally near the beam source 52,to improve its radiation emission efficiency and prolong its effectiveradiation lifetime.

The charged particle beam 54 generated by the charged particle source 52may initially have radially outward diverging properties whiletravelling along the optical axis A. The collimator electrode stack 70may then serve to refract portions of the charged particle beam 54selectively, thereby collimating the beam i.e. making the various partsof the beam distribution travel downstream with greater co-linearityalong the optical axis A.

Collimator stack 70 comprises an axially arranged stack (i.e. sequence)of collimator electrodes 71-80 that are mutually displaced along theaxial direction Z by means of spacing structures 89, which are made ofan electrically insulating material. The collimator electrodes 71-80 areformed by flat ring-shaped bodies 81, each of which comprises anelectrode aperture 82. In the shown embodiment, the ring-shaped bodies81 are displaced at equal distances Hd along the optical axis A, and theelectrode apertures 82 are coaxially aligned along the optical axis A.The electrode bodies 81 are preferably made of an electricallyconducting and mechanically rigid material. Sufficient electricalconductivity enables easy application of a homogeneously distributedelectrical charge onto each respective surface of the collimatorelectrodes 71-80. Sufficient mechanical rigidity allows the collimatorelectrodes 71-80 to retain a fixed spatial configuration and hence tosustain steady electric potential differences during generation of theparticle beam 54. Preferably, the electrodes 71-80 are made fromaluminum. Aluminum is a light-weight material with good electricalconductance and non-magnetic properties, and which furthermore providessufficient thermal conductance for dissipating thermal energy that isaccumulated during charged particle beam generation.

The formation of a plurality of collimator electrodes 71-80 and spacingstructures 89 into a coaxially aligned electrode stack 70 provides thepossibility to optimize the electric field distribution within thecollimator stack 70 at different positions along the optical axis A. Theuse of a plurality of separated collimator electrodes 71-80 allows for arelatively lightweight design.

Thicknesses H1, H5, He of the collimator electrodes 71-80 along thevertical direction Z may be sufficient for accommodating a liquidconduit 105 on an inside of respective electrode bodies 81, whileensuring sufficient structural integrity of the electrode body 81 duringbeam generation, even under considerable thermal stresses.

An uppermost collimator electrode 71 in the collimator stack 70 (i.e.the collimator electrode 71 that is encountered and traversed first bythe charged particle beam 54 upstream of the stack 70) comprises adiverging curved aperture. A last collimator electrode 80 in thecollimator stack 70 (i.e. the collimator electrode that is encounteredlast by the charged particle beam 54 downstream along the optical axisA) has a relatively small inner thickness H10. Electrode properties ofthe stack are further discussed with reference to FIG. 6.

The collimator electrodes 71-80 are spaced with respect to each other bymeans of the electrically insulating spacing structures 89. The spacingstructures 89 define a minimal distance Hd between the electrodes 71-80,which prevents the occurrence of electrical discharge between adjacentelectrodes, even at relatively large electrical potential differencesthat are to be applied between the electrodes during beam generation(potential differences in the order of kilovolts per millimeter).

The spacing structures 89 are made of an electrically insulatingmaterial that also has a high resistance to mechanical compression, tokeep the distances between the electrodes fixed, and to avoid theelectrodes from becoming electrically connected (i.e. becomingelectrical equipotential surfaces). The spacing structures 89 may forexample be made of a ceramic. Preferably, each spacing structure 89 isprovided between a pair of adjacent collimator electrodes. Three suchspacing structures 89 are provided between each pair of adjacentcollimator electrodes, to provide two stable 3-point support planes, onefor each adjacent collimator electrode, while maintaining a well-definedinter-electrode spacing Hd.

The collimator stack 70 is suspended within the beam generator chamber51 by means of support protrusions 92 b and support legs 93 thatsurround the stack 70 on three sides. The support legs 93 are used tofix the collimator stack 70 with respect to an external reference frame(e.g. carrier frame 42).

Embodiments of the cooling arrangement (e.g. comprising elements 110-114and 116-119) are described herein below, in conjunction with FIGS. 7a -7d,

FIG. 4 shows a perspective view of a collimator electrode stack 70according to an embodiment. This embodiment comprises ten collimatorelectrodes 71-80 for shaping the electron beam 54 propagating along theoptical axis A in the axial direction Z.

The first collimator electrode 71 comprises source engagement membersfor fixing the charged particle beam source 52 to the first collimatorelectrode 71 on a top side thereof, and source alignment members foraligning the optical axis A of the generated charged particle beam 54with a centerline of the collimator apertures.

Each of selected collimator electrodes 71-74, 76-80 comprises threesupport portions 86 along an outer electrode perimeter. Each supportportion 86 accommodates a spacing structure 89 on one side, and possiblyanother spacing structure 89 on the opposite side. In this embodiment,the spacing structures 89 are formed by cylindrical objects with flatend surfaces that support or are supported by the electrode supportportions 86. Cylindrical spacing structures 89 with uniform diametersare easy to manufacture in large numbers, which facilitates constructionand maintenance of the collimator stack 70. In addition, the roundedshape of the cylindrical spacing structures 89 helps to reduceperturbing effects of the spacing structures on the electric fieldinside the electrode collimator stack 70. Construction of the collimatorstack 70 is further facilitated and standardized by manufacturingspacing structures 89 with a uniform predetermined spacer height Hs.This allows all collimator electrodes 71-80 to be efficiently alignedand spaced over equal predetermined mutual distances Hd along the axialdirection Z.

In the shown embodiment, three of such electrically insulatingcylindrical spacing structures 89 are arranged between each adjacentpair of electrodes. Three spacing structures 89 form a radially andangularly equally spaced tripod i.e. each spacing structure 89 islocated at an equal radial distance from the optical axis A, and thethree spacing structures 89 are mutually spaced at 1800 angles about theoptical axis A. The resulting three-point support allows the collimatorelectrodes to be carried along their respective transversal planes in astable manner, and allows electrode alignment with a high accuracy(typically with a maximum alignment error below 10 micrometers). Theequal radial and/or angular spacing is not essential, but yields apreferred robust arrangement that facilitates accurate collimatoralignment.

The electrode support portions 86 of adjacent collimator electrodes andinterposed spacing structures 89 are axially aligned to define supportcolumns 90 directed parallel with the axial direction Z. Three supportcolumns 90 are defined in this embodiment.

The support columns 90 are each provided with clamping members 91 a, 91b, for holding the support portions 86 and interposed spacing structures89 together. Ledgers 91 a are provided at axial extremities of thesupport columns 90. The ledgers 91 a arc pulled together along the axialdirection Z by means of two pre-tensioned rods 91 b that connect theledgers 91 a at the rod ends. The clamping members 91 a, 91 b are madeof a rigid material that has sufficient tensile strength to provide arobust clamping mechanism with which the collimator electrodes 71-80 andspacing structures 89 can be axially compressed into mutually fixedpositions. Each pre-tensioned rod 91 b may be provided with a narrowing91 c, to accommodate differential thermal expansion between thecollimator stack 70 and the respective pre-tensioned rod 91 b. Theclamping members 91 a, 91 b are preferably made of a non-magneticmaterial, to avoid generation of perturbing field responses to themagnetic fields generated by the charged particle beam 54. In view ofthe above, the clamping members 91 a, 91 b are preferably made oftitanium.

The collimator electrode stack 70 comprises three stack support legs 93.Each support leg is connected to a middle region 75 a of the collimatorstack 70. The support legs 93 cooperate to support the collimator stack70 with respect to an external reference frame. The external referenceframe may for example be the carrier frame 42 suspended inside thevacuum chamber 30 of the charged particle lithography system 10 shown inFIG. 1.

During beam generation, mechanical resonances may be induced within thecollimator stack 70 from external sources (e.g. from floor vibrationsthat reach the collimator stack 70 via the carrier frame 42, and fromflow fluctuations occurring in cooling liquid that is pumped throughcooling conduits 105 in the collimator electrodes 71-80). By supportingthe collimator stack 70 via connection of the support legs 93 to themiddle region 75 a, the lengths and weights of stack portions thatparticipate in induced mechanical resonances are reduced.

The induced mechanical resonances may relate either to linear motion, torotational motion, or to both. By reducing the effective stack lengths,the effective linear spring constant for deflections perpendicular tothe axial direction Z is increased, as shorter columns 90 make stiffercolumns. Stiffer columns reduce transversal deflection response of theelectrodes 71-80 in the stack. With stiffer columns 90, the electrodes71-80 will vibrate less with respect to each other, and hence vibrateless with respect to the environment, which will ultimately improve thebeam projection accuracy.

Furthermore, by engaging the stack approximately halfway at the verticalcenter of mass of the stack, the moments of inertia for the stack as awhole and about rotation axes in the transversal plane are reduced,which also reduces rotational deflection response of the stack as awhole to externally driven lower frequency torque oscillations.

In the embodiment shown in FIG. 4, the middle region 75 a of thecollimator stack 70 (i.e. the vertical center of mass) is selected tocorrespond to the middle collimator electrode 75 of the collimator stack70. Here, the middle electrode 75 is formed by the fifth collimatorelectrode 75 counted downstream from the source 52 (not shown in FIG. 4but in FIG. 3. The preference here for the fifth electrode as the middleelectrode (in contrast to e.g. the sixth electrode 76) relates to theadditional weights of the thicker first electrode 71 and the source 52to the stack 70.

The middle collimator electrode 75 comprises an electrode body 92 a thatis provided with three stack support protrusions 92 b along the outerelectrode perimeter. Radially extending stack support protrusions 92 balong the outer perimeter of the middle electrode 75 provide a robustsupport construction that may be easily manufactured e.g. via uni-bodycasting of the middle electrode 75. The electrode body 92 a andprotrusions 92 b have sufficient mechanical strength for jointlysupporting a total weight W of the collimator electrode stack 70. Eachstack support leg 93 is connected to a respective stack supportprotrusion 92 b.

In alternative embodiments (not shown), the support legs 93 may engagewith the spacing structures 89 in the support columns 90 (alternative orin addition to engaging the middle collimator electrode 75) to establisha balanced supporting connection with the external reference frame.

In the embodiment of FIG. 4, each stack support leg 93 comprises a legjoint 94 for connecting the support leg to the middle stack region 75 a(e.g. to support protrusion 92 b). Furthermore, each stack support leg93 comprises a leg base 95 for connecting the support leg 93 to theexternal reference frame. Near the leg base 95, the stack support leg 93has a triangular support structure with separate leg members 93 a-93 bdirected at least partially along opposite angular directions. The legmembers 93 a-93 b may be made of mechanically rigid but electricallyinsulating material. Above and below these leg members 93 a-93 b, eachsupport leg 93 comprises two radial deflection portions 96 a-96 b forallowing the leg joint 94 to displace in the radial direction R withrespect to the leg base 95. In the embodiment of FIG. 4, the radialdeflection portions 96 a-96 b comprise beams with a cross-section havinga curved I-profile defining a flexible narrow middle region. Each beamis substantially oriented perpendicular to the (local) radial direction,thereby allowing the I-profile to flex only within the localradial-axial plane, while remaining mechanically stiff in the localangular direction. The allowed radial displacements between the legjoints 94 and corresponding leg bases 95 may for example result fromradially directed thermal deformation of the middle stack region 75 a(e.g. middle electrode 75) with respect to the leg bases 95 during beamgeneration. The middle collimator electrode 75 is envisioned to be heldat a relatively high positive electrical potential during beamgeneration, which will result in a large number ofsecondary/backscattered electrons impacting on this middle electrode 75.The resulting heating will cause radial expansion of the collimatorelectrode 75, while the external reference frame will not experiencesuch thermal deformation. The differential radial deformation can beefficiently accommodated by the radial deflection portions 96 a, 96 b,and radial tilting of the leg members 93 a-93 b between these deflectionportions 96 a, 96 b.

In alternative embodiments (not shown), the support system may also bedifferently shaped. For example, additional leg segments may be includedabove and/or below the triangular structures with leg members 93 a-93 b,in order to form e.g. A-shaped support legs. Furthermore, the radialdeflection portions 96 a-96 b may be formed differently, e.g. having adifferent cross-sectional profile.

According to various embodiments, the external reference frame (e.g.carrier frame 42) may support the electrode stack 70 in the middleregion 75 a via support members 93 that may be oriented in any of adownward axial direction Z (compression stresses exerted on support legs93; shown in FIG. 4), an upward axial direction −Z (tensile stressesexerted on support members 93; not shown), a radial direction R (bendingstresses on support members 93; not shown), or combinations thereof.

FIG. 5 shows a perspective view of an embodiment of an intermediatecollimator electrode 72-74, 76-79. The intermediate collimator electrode72-74, 76-79 is formed by a flat electrode body 81 made of electricallyconducting and mechanically rigid material, with a collimator aperture82 provided at a center of the flat body 81. The collimator aperture 82is substantially circular as viewed along the axial direction Z, anddefines an inner aperture diameter Ø. Furthermore, the circular aperture82 has a rounded (i.e. a curvedly trimmed) aperture perimeter 82 a,viewed in a cross-section along the angular direction Φ (i.e. across-section in an axial-radial plane). The rounded aperture perimeter82 a helps to avoid high local electric field concentrations along theaperture perimeter 82 a. The rounded aperture perimeters 82 a may beshaped to avoid generation of local electric field strengths above 5kilovolts per millimeter.

The collimator electrode 71-80 comprises three support portions 86 alongan outer electrode perimeter 85. Each support portion 86 is configuredto accommodate one spacing structure 89 on one side (e.g. for the firstand last electrodes 71, 80) or spacing structures 89 on each side (e.g.for the intermediate electrodes 72, 73, 74, 76, 77, 78, 79).

The spacing structures 89 between the collimator electrodes 71-80preferably have equal heights Hs along the axial direction Z. Spacingstructures 89 with an equal height facilitates manufacturingstandardization for the spacers 89, as well as for other structures thatare to be attached between collimator electrodes (e.g. intermediatecooling conduits, discussed below). Preferably, a spacer height Hs issmaller than one third of a shortest radial distance ΔR1 from thecollimator aperture perimeter 82 a to a lateral surface of a nearbyspacer 89. Electric field perturbations at the collimator aperture 82due to the presence of the spacer structures 89 are thereby reduced tonegligible levels.

The collimator electrode 71-80 is provided with three electrode supportarms 87 along an outer electrode perimeter 85 of the electrode platebody 81. The three electrode support arms 87 are preferably distributedequally spaced around the outer electrode perimeter 85 (at equaldistances along the angular coordinate). The electrode support arms 87slightly protrude radially along the outer perimeter 85, and extendsubstantially along the angular direction (D. Each electrode support arm87 may comprise at least one rigid arm portion 87 a that is connected onone distal end via a flexible arm narrowing 87 b to the outer perimeter85 of the electrode body 81. Each electrode support arm 87 may beconnected on its opposite distal end to a corresponding electrodesupport portion 86. Each electrode support portion 86 may be formed by acircular platform. A second flexible arm narrowing 87 c may be providedbetween the rigid arm portion 87 a and the electrode support portion 86.The rigid arm portion 87 a and the flexible arm narrowings 87 b-87 cpreferably have a height along the axial direction that is identical orat least comparable to a height of the corresponding collimatorelectrode, so as to provide sufficient mechanical stiffness/strength forsupporting the collimator electrode in the axial direction Z. Thenarrowing provided in each of the flexible arm narrowings 87 b-87 c ispredominantly defined in a direction in the radial-angular plane, andmore preferably directed along the (local) radial direction R. In thisembodiment, the flexible arm narrowings 87 b-87 c effectively form leafsprings that mainly allow deformation and flexing of the correspondingelectrode support portion 86 with respect to the electrode body 81 inthe radial-angular plane, while preventing flexing of the correspondingelectrode support portion 86 with respect to the electrode body 81 inthe axial direction Z. Each electrode support arm 87 defines a thermalexpansion slot 88 between the electrode support body 81 and theelectrode support arm 87. The thermal expansion slot 88 also extends inthe radial-angular plane and substantially along the angular direction(D.

The radially movable arm 87 with its one or more flexible arm narrowings87 b-87 c as well as the thermal expansion space 88 enable the electrodebody 81 to deform (expand/contract) predominantly in the radial-angularplane, and more particularly in the radial direction R, while keepingthe support portions 86 axially aligned with corresponding supportportions 86 of adjacent collimator electrodes. It is expected thatduring use of the collimator electrode stack 70, the collimatorelectrodes 71-80 will be held at different electric potential values,and receive different amounts of (secondary/backscatter) electronradiation and of resulting thermal energy. The movable arms 87 andexpansion spaces 88 efficiently accommodate for the varying anddifferent thermally induced radial deformations of the electrodes 71-80occurring during generation and collimation of the charged particle beam54, whereby the support columns 90 (see FIG. 4) remain mutually alignedalong the axial direction Z.

The middle collimator electrode 75 and adjacent intermediate collimatorelectrodes in the embodiment shown in FIG. 4 are designed to besubjected to large positive electric potentials during beam generation.Also, the last electrode 80 in the stack 70 is designed to be subjectedto a considerable electric potential (in the order of +0.5 to +1.5kilovolts). The resulting considerable attractive forces that any ofthese electrodes will exert on secondary electrons and backscatteredelectrons will give rise to a significant electron collision andabsorption, and hence to a considerable heat generation. For example,radial expansion of the middle collimator electrode 75 will force theelectrode support columns 90 to move radially outward, which will pullthe support portions 86 of other collimator electrodes outwards.However, the radially movable support arms 87 provided on the remainingcollimator electrodes will accommodate for this radial expansion,thereby keeping all electrodes 71-80 coaxially aligned.

FIG. 6 shows a schematic cross-sectional side view of a collimatorelectrode stack 70 according to an embodiment. The collimator electrodestack 70 comprises ten collimator electrodes 71-80, wherein the fifthcollimator electrode 75 constitutes the middle collimator electrode. Theshown cross-section only schematically depicts several characteristicdimensions of this embodiment of the collimator electrode stack 70. Manyconstruction details of this embodiment are omitted for simplicity (forexample, detailed shapes of collimator apertures, electrode supportportions, and spacing structures are not shown)

In general, the use of multiple collimator electrodes 71-80 separated byspacing structures 89 so as to form a coaxially arranged collimatorelectrode stack 70 provides the possibility for optimizing the electricfield distribution in the collimator stack 70 at different positionsalong the optical axis A. The step-wise variation of the electricpotential differences between at least five adjacent collimatorelectrodes results in a relatively smoothly varying electric fielddistribution along the axial direction A. An electrode stack comprisingfive or more collimator electrodes allows generation of an electricfield distribution that may have a plurality of negative electric fieldminima as well as a plurality of positive electric field maxima, andhence yields sufficient degrees of freedom for generating electricfields that may both collimate a charged particle beam 54 as well asreduce spherical aberrations in the charged particle beam 54. Findingpreferred beam characteristics for a particular application is achievedeasily with the multi-collimator electrode stack via variation of theapplied electrical potential values.

The inventors noted that, in one particular embodiment, the use of tencollimator electrodes 71-80 in a collimator stack 70 provides a goodbalance between the degrees of freedom for creating a relatively gradualelectrical potential distribution along the axial direction Z on onehand, and obtaining sufficient inter-electrode spacing Hd for providinga good line of sight with vacuum pumps 122, 123, sufficient electrodecooling, and constructional simplicity on the other hand.

In the embodiment of the collimator electrode stack 70 shown in FIG. 6,the intermediate electrode thicknesses He of all the intermediatecollimator electrodes 72, 73, 74, 76, 77, 78, 79 are substantiallyidentical. The term “substantially identical” herein refers tointermediate electrode thicknesses He that have the same value withinachievable manufacturing tolerances. For collimator electrodes made fromaluminum, the intermediate electrode thickness He may be in the range of10 millimeters to 20 millimeters, preferably in the range of 12millimeters to 15 millimeters, and more preferably equals 13.6millimeters. Using intermediate electrodes of equal thickness allowsmass production of the electrode bodies and simplifies the assembly ofthe intermediate collimator electrodes into a collimator stack. Inalternative embodiments, all of the electrodes may have identicalthicknesses. Yet in other embodiments, some or all of the electrodethicknesses may be different.

An uppermost collimator electrode 71 in the collimator stack 70 (i.e.the collimator electrode 71 that is encountered and traversed first bythe charged particle beam 54 upstream of the stack 70 and along theoptical axis A) comprises a smaller upper aperture diameter Ø1, followedby a divergently curved aperture bore 71 a. The small upper aperturediameter Ø1 and curved aperture bore 71 a allow a charged particle beam54 generated by the beam source 52 to experience a gradual electricfield change. A first electrode thickness H1 of the first collimatorelectrode 71 is in a range defined by 1.5·He≤H1≤2.5·He. A firstcollimator electrode 71 having a thickness in the specified range allowsthe upstream end (i.e. the top) of the collimator stack 70 to have asmooth transition from a relatively small beam source aperture, to therelatively larger collimator apertures, and allows the first electrodeto have sufficient strength for directly supporting a weight of the beamsource 52 that is mountable thereon. The term “smooth” is used herein toindicate that a surface (here, the aperture surface) has no abruptchanges in curvature (i.e. sharp ridges, corners, or crevices) at amacroscopic scale. Abrupt curvature changes would generate undesirablylarge local variations in the electric field.

A middle collimator electrode 75 is provided between the firstcollimator electrode 71 and the last collimator electrode 80. Theintermediate collimator electrodes 72, 73, 74, 76, 77, 78, 79 arelocated between the first collimator electrode 71 and the lastcollimator electrode 80, and on both sides of the middle collimatorelectrode 75. A middle electrode thickness H5 of the middle collimatorelectrode 75 is in a range defined by 1.5·He≤H5≤2.5·He. Preferably, themiddle electrode thickness H5 ties in a range between 22 millimeters to26 millimeters, and more preferably equals 24 millimeters. A middlecollimator electrode 75 having a thickness H5 in the specified rangeallows the center region 75 a of the collimator stack 70 to havesufficient strength and bending stiffness for preventing the collimatorelectrode stack 70 from vibrating e.g. about transversal axes(perpendicular to the axial direction Z).

In alternative embodiments, the middle electrode 75 may have a thicknessH5 that is substantially equal to the thickness He of the intermediateelectrodes 72-74, 76-79. This may for example be achieved by the use ofmechanically stronger materials, or in the case that the stack supportstructure engages other and/or more electrodes in the collimator stack.This is further explained with reference to FIG. 15.

The last collimator electrode 80 in the collimator stack 70 (i.e. thecollimator electrode that is encountered last by the charged particlebeam 54) has a radially inner portion 80 a with a last electrode innerthickness H10. The inner thickness H10 lies in a range defined byH10<He/3. The inner thickness H10 of the last electrode 80 preferablyhas a relatively small value to effectively sustain an electricpotential with opposite polarity with respect to the charged particlebeam 54 while extending over only a small axial distance. This producesa highly localized attractive E-field near the aperture perimeter. Thethin last electrode 80 with opposite polarity produces negativespherical aberration for a beam of charged particles, to compensate forpositive spherical aberrations in the beam that have been generated inthe preceding part of the collimator stack 70.

The last collimator electrode 80 has a last electrode outer thicknessH10′ at a radially outer portion 80 b. The last electrode outerthickness H10′ preferably equals the intermediate electrode thicknessHe, to make the last electrode 80 mechanically stronger, and also toprovide sufficient height for accommodating a cooling conduit inside theoutward portion. As shown in FIG. 6, the transition from the innerportion 80 a to the outward portion 80 b may involve an axial stepwiseincrease from inner thickness H10 to outer thickness H10′. This createsan inner aperture diameter Ø10 for the radially inner portion 80 a, andan outer aperture diameter Ø10′ for the radially outer portion 80 b.According to a preferred embodiment, the inner body thickness H10 of thelast collimator electrode 80 is in a range of 5 millimeters or smaller,the outer body thickness H10′ is in a range of 10 millimeters or larger,the inner aperture diameter Ø10 is 60 millimeters, and the outeraperture diameter Ø10′ is 100 millimeters.

Downstream of the last electrode 80, there is provided an aperture array58 for forming a plurality of beamlets from the charged particle beam54. The aperture array 58 may be a structural component of thecollimator electrode stack 70. Alternatively, the aperture array 58 mayform part of a condenser lens module 56 that is arranged in theprojection column 46 directly downstream from the beam generator module50 (as viewed along the optical axis A). The aperture array 58 comprisesa lower central surface and slanted lateral surfaces. During operation,the aperture array 58 is preferably kept at ground potential. The shapeof the aperture array 58 creates sufficient distance between the innerperimeter of the (relatively) thin radially inner electrode portion 80 aof the last collimator electrode 80, to avoid electrical dischargingbetween the (sharp edges of the) charged last collimator electrode 80and the aperture array 58. The shape of the aperture array 58 alsoensures that the spacing between the aperture array 58 and the radiallyoutward electrode portion 80 b of the last collimator electrode 80 iskept small, to preserve the vacuum inside the collimator electrode stack70 with respect to the region outside the beam generator module 50and/or outside the condenser lens module 56.

FIG. 6 helps to illustrate exemplary methods for operating thisembodiment of the collimator electrode stack 70 during beam generationand processing. In this embodiment, the collimator electrodes 71-80 arepositioned at equal distances Hd along the optical axis A in a coaxialarrangement.

In other embodiments, the collimator electrodes may be positioned atdifferent inter-electrode distances. See for example the embodimentsdiscussed with reference to FIGS. 9-11.

Different electrostatic potential values (i.e. voltages) are applied tothe collimator electrodes 71-80. The collimator electrode stack 70, thecharged particle beam generator 50, or the charged particle lithographysystem 10 may comprise a set of distinct voltage sources 151-160. Eachvoltage source 151-160 comprises an output terminal for applying aselected electric potential to a respective collimator electrode 71-80.An electric connection is provided between the output terminal of eachvoltage source 151-160 and the electrical contact 109 of a correspondingcollimator electrode 71-80. Preferably, the voltage sources 151-160 areindependently and dynamically adjustable during operation of the beamgenerator 50. Alternatively, the voltage sources 151-160 may be formedas a single power supply with suitable adaptors and dividers to convertits output(s) to distinct selected voltage values to be applied to thecorresponding collimator electrodes 71-80.

Below, is a table of two numerical simulations (one per column), whichcorresponds to a preferred arrangement for the collimator electrodes,and to two preferred electric potential distributions applied to theelectrodes 71-80. The sequence of electrode numbers in the tablecorresponds to the sequence of collimator electrodes 71-80 as used inthe description with reference to e.g. FIGS. 4 and 6.

V-distribution V-distribution 2 Electrode # 1 (along Z) (along Z) 71 0 V0 V 72 −3165 V −3649 V 73 5577 V 3907 V 74 23160 V 19140 V 75 29590 V21990 V 76 17400 V 9651 V 77 4870 V 1525 V 78 698 V −313.5 V 79 52 V−491.9 V 80 1023 V 702.2 V

The listed electric potential values for the various electrodescorrespond to potential differences with respect to ground potential.Each of the electric potential values may be applied to the collimatorelectrodes 71-80 by the corresponding voltage source 151-160. Duringoperation, the aperture array 58, which is located directly downstreamof the last collimator electrode 80, is preferably kept at groundpotential. A method for operating a charged particle beam generator 50may comprise:—generating an electron beam 54 with the beam source52;—projecting the generated electron beam along an optical axis Athrough the apertures 82 of the collimator electrode stack 70;—applyingelectrical potentials onto the collimator electrodes 71-80,comprising:—keeping a first collimator electrode 71 at groundpotential;—keeping a middle collimator electrode 75 at a highestpositive electric potential, and—keeping a last collimator electrode 80at a low positive electric potential.

The electric potential differences applied across the collimatorelectrodes serve to produce a homogeneous transversal electron beamsurface current density, while reducing the angular error. During beamgeneration, the electron beam 54 emanates from the beam source 52 with alocally diverging contour as viewed in a cross section in a radial-axialplane.

The strongly increasing electric potential values applied to the third,fourth, and fifth collimator electrodes 73-75 creates a local electricfield distribution that acts as a positive lens on the traversingelectron beam 54. This serves to refract the local contour of theelectron beam 54 in the radial-axial cross-section towards the opticalaxis A, and causes the distribution of the electron beam 54 to converge.Due to the radial variation of the electric field strength in theradial-angular plane, the positive lens effect may cause the electronsin the electron beam 54 to obtain a non-uniform axial speed distributionas viewed in the radial-angular plane (which causes for sphericalaberration effects).

The strongly decreasing electric potential values applied to the sixth,seventh, eighth, and ninth collimator electrodes 76-79 create a localelectric field distribution that acts as a negative lens on thetraversing electron beam 54. This also refracts the local contour of theelectron beam 54 in the radial-axial cross-section, but now away fromthe optical axis A. The variations in the radial distributions of theelectron beam and the electric field may again contribute to sphericalaberration effects.

A positive electric potential (with respect to a grounded reference)applied to the last collimator electrode 80 produces negative sphericalaberration in the traversing electron beam 54 (or for a beam ofnegatively charged particles in general). The generated negativespherical aberrations will (at least partially) compensate any positivespherical beam aberration that has been generated in the preceding partof the collimator stack 70.

The voltage sources 151-160 are preferably set to create electricpotentials on the collimator electrodes 71-80 so that a final localcontour of the electron beam 54 is properly collimated as it emanatesdownstream from the beam generator 50 (i.e. the beam is made parallel inthe radial-axial cross-section, at least as much as possible). Theelectric potentials created by the voltage sources 151-160 may bedynamically adjusted, in order to alter the distribution of theelectrical potential values along the axial direction and/or to alterthe local amplitudes of the electric fields. The axial centers of thepositive and negative lenses may thus be moved along the axialdirection, and/or the field amplitudes changed. The independentadjustability of the electric potentials applied to the collimatorelectrodes 71-80 during operation facilitates reconfiguration andoptimization to changing operational conditions (e.g. beam current,vacuum conditions, shielding conditions, etc.)

The method may further comprise:—keeping a second collimator electrode72 preceding the middle electrode 75 at a negative electric potential.In addition, the method may also comprise—keeping at least one of twointermediate collimator electrodes 78, 79 directly preceding the lastcollimator electrode 80 at low negative electric potentials. Applying anegative electric potential at one or two of the last intermediatecollimator electrodes 78-79 preceding the last collimator electrode 80helps to deflect secondary electrodes and/or backscattered electrodesoriginating from a region downstream of the collimator electrode stack70. Secondary electrons may for example be created during collisions ofprimary electrons in the electron beam 54 with the aperture array 58.The local negative electric potential helps to reduce the number ofelectrons that impact on the strongly positively charged middlecollimator electrode 75.

According to the above mentioned specific numerical examples, furtherembodiments of the method for operating a beam generator 50 maycomprise:—keeping at least one of two intermediate collimator electrodes78, 79 directly preceding the last collimator electrode 80 at a fixedelectric potential with a value of −300 Volts to −500 Volts;—keeping thesecond collimator electrode 72 at a fixed electric potential with avalue of −3 kilovolts to −4 kilovolts;—keeping the middle collimatorelectrode (75) at a fixed electric potential with a value of +20kilovolts to +30 kilovolts, and—keeping a last collimator electrode 80at a positive potential in a range of +500 Volts to +1100 Volts.

FIGS. 7a-7d show cross-sectional top and side views of collimatorelectrodes 71-80 according to embodiments. The shown collimatorelectrodes 71-80 are provided with a cooling conduit 105 fortransferring a cooling liquid 102, the cooling conduit 105 comprising afirst opening 103 for connection to a liquid supply structure 117, and asecond opening 104 for connection to a liquid discharge structure 118.

The presence of a cooling conduit 105 may further improve the accuracyand reliability of electric field control, as thermally induceddeformation of the collimator electrode 71-80 may be regulated. Thecooling conduit 105 may reduce expansion of the collimator electrode71-80 due to thermal heating, for example caused by exposure toscattered and/or secondary electrons. Electrical conductance within thecooling liquid 102 is to be minimized, to avoid electrical chargeaccumulated on at least one of the collimator electrodes to betransported toward other collimator electrodes in quantities that aresufficiently large to alter the electrical potentials applied to theelectrodes. Although more powerful charge sources may be used tocompensate for any charge transport via the cooling liquid, such chargedissipation is less desirable due to the resistive heating from theresulting current through the cooling liquid, which negativelyinfluences the liquid's cooling capacity. Electrical separation may beachieved by using ultra-pure water (UPW) or non-conducting oil as acooling liquid. Preferably, UPW is constantly or intermittently filteredduring operation of the particle beam generator 50.

As shown in FIGS. 7a-7d , the collimator electrodes comprise aring-shaped electrode body 81 (primes for the various embodiments areimplied wherever applicable) provided with a top surface 83 facing thecharged particle source 52, and a bottom surface 84 facing away from thecharged particle source 52. The bottom surface 84 and top surface 83 areconnected to each other via a side surface 85, which defines an outerelectrode perimeter. The first opening 103 and the second opening 104are located in the side surface 85. Locating the first opening 103 andthe second opening 104 of the cooling conduit 105 in the side surface 85helps to keep the space between the different collimator electrodes71-80 in the stack 70 free from potentially interfering (i.e. electricfield perturbing) structures. In particular, since the cooling liquidsupply and/or removal occur from a lateral side of the electrodes 71-80,the liquid supply structure 117 and/or liquid removal structure 118 donot need to occupy any space between the collimator electrodes 71-80.

The first opening 103 and the second opening 104 are located at the sameside of the collimator electrode 71-80. Locating the first and secondopenings 103, 104 at the same side allows for placement of both thecooling liquid supply structure 117 and the cooling liquid dischargestructure 118 at the same side of the collimator stack 70, whichprovides more space for other components to be placed alongside/aroundthe collimator stack 70.

The cooling conduit 105 connects the first opening 103 with the secondopening 104 along a trajectory running through the electrode body 81around the electrode aperture 82. The cooling conduit 105 comprises asubstantially circular portion 105 a around the aperture 82 and twosubstantially straight end portions 105 b for connecting the circularportion 105 a with the first opening 103 and the second opening 104.This arrangement is particularly favorable if the electrode aperture 82is a circular aperture. Here, the substantially circular conduit portion105 a traces out a trajectory at a constant distance from the apertureperimeter 82 a, which results in more homogeneous cooling of the centerportion of the collimator electrode 71-80.

The cooling conduit 105 is formed by a tubular structure, with tubeopenings 103, 104 that are oriented in radial directions. A relativelystrong thermally and electrically conductive material is preferred asconstruction material for the cooling tube. Titanium for example, is astrong metal non-magnetic metal. A titanium cooling tube 105 providedin/on the collimator electrode body 81 will not generate significantmagnetic field disturbances or magnetic stresses in response to the fluxof the (nearby) charge particles travelling along the optical axis.Furthermore, titanium has a relatively high melting temperature (about1940 Kelvin), which makes it a very suitable metal for manufacturingcooling conduits 105 inside a collimator electrode, by casting thecollimator electrode body 82 from a metal of a substantially lowermelting point (e.g. aluminum, having a melting temperature at about 930Kelvin) around the titanium cooling tube 105. Alternatively, molybdenummay be used as a material for constructing the cooling tubes.

The cooling tube 105 may have a circular cross section, for achieving arelatively homogeneous liquid flow inside. An outer diameter of such acircular cooling tube 105 may be in the range of 0.6 centimeter to 1centimeter, and a corresponding inner diameter in the range of 0.4centimeter to 0.8 centimeter.

As shown in FIG. 7a , the conduit tube 105 may be integrated (e.g. cast)within the body 81 of the collimator electrode 71-80. Integral formationimproves the cooling efficiency. Furthermore, by integrating the tubeswithin the electrode, the tubes will not protrude from the body surfaceand create local electric field concentrations, which would otherwiseperturb the desired field distribution across the electrode aperture 82.The probability for sparking between the electrodes 71-80 is alsoreduced (which would not be the case for conduit tubes positioned on topof or protruding from the electrode surface). Moreover, having conduittubes 105 integrated within the collimator electrode body 81 willincrease the lateral space (i.e. mean free path) available for freemolecules moving in the collimator stack 70 to travel radially outwardand be removed e.g. absorbed by getter pumps 122, 123 positionedradially outward at a distance from the collimator stack 70. In the casethat thermal heat transfer efficiency between the collimator electrodeand the cooling liquid 102 has to be maximized, it is preferred that theelectrode is formed via casting of electrode material around the coolingconduit 105.

The circular portion 105 a the conduit tube 105 is preferably located ata sufficient radial conduit distance ΔR2 away from the apertureperimeter 82 a of the electrode aperture 82. This ensures that thecooling effect of the cooling liquid 102 flowing through the circularportion 105 a of the cooling conduit 105 stays relatively homogeneousalong the angular coordinate (i.e. the temperature difference betweenthe inflowing liquid and outflowing liquid stays relatively small), sothat the differential thermal expansion of the electrode body 81 staysroughly the same as a function of the angular coordinate.

For example, for collimator stack embodiment with aluminum collimatorelectrodes (with a typical bulk thermal conductivity of 237 Watts permeter Kelvin) comprising electrode apertures 82 with an aperturediameter Ø of about 60 millimeters, which have an electrode thickness ofabout 13.6 millimeters, which accommodate a flow of water as coolingliquid, and in which at least one of the collimator electrodes is heatedup with a temperature increase of up to 60° C. during operation, theradial conduit distance ΔR2 is preferably chosen to be 20 millimeters orlarger. Note that in this example, a typical total diameter of thecircular conduit portion 105 a will be 100 millimeters or larger.

Alternatively, as shown in FIG. 7c , the conduit tube 105 may beaccommodated inside a recess 106 provided in the electrode body 81′ on atop side 83′ thereof. Milling a recess 106 into the electrode body 81′and placement of the conduit tube 105 therein is a relatively cheapmethod for manufacturing a electrode. A thermally conducting adhesivematerial 107 may be provided in the recess 106 around the cooling tube105, in order to fix the tube to the electrode body 81′ and increase theeffective thermal transfer interface. Attaching the conduit tube in therecess will also reduce local mechanical resonances propagating alongthe tube 105.

In yet another embodiment, which is shown in FIG. 7d , the conduit tube105″ may have a rectangular outer cross section, i.e. a rectangularouter perimeter as viewed in a cross-section along the radial-axialplane. This conduit tube 105″ is also accommodated inside a recess 106′provided inside the electrode body 81″ and with an opening on a top side83′ thereof. The recess 106′ is provided with a complementaryrectangular contour in an (axially) inner portion of the recess, toaccommodate the rectangular conduit tube 105″ in a manner that improvesthe thermal contact between lower and lateral sides of the conduit tube105″ on the one hand, and the lower and lateral sides of the recess 106′on the other hand. In this embodiment, the conduit tube 105″ comprises alower gutter portion 105 c with a curved inner void for accommodatingthe cooling liquid 102″, and a flat upper lid portion 105 d for closingthe curved inner void in a sealing manner (e.g. by laser welding theupper lid portion 105 d onto upright lateral walls of the lower gutterportion 105 c). An (axially) outer portion of the recess 106′ may have afillet (rounded) shape, to facilitate insertion of the conduit tube 105″into to recess 106′.

In any of the embodiments, intermediate conduits (e.g. tubular elements)110 are provided for connecting a second opening 104 of a collimatorelectrode with a first opening 103 of a subsequent collimator electrodeof the electrode stack 70. Using intermediate tubular elements 110provides the ability to cool more than one collimator electrode withinthe collimator stack 70, while only a single cooling liquid supplystructure 117 and cooling liquid removal structure 118 are needed forsupply and removal of cooling liquid respectively. If more than onecollimator electrode of the collimator electrode stack 70 is to becooled, this embodiment is relatively easy to implement.

In the embodiment of FIG. 3, the intermediate tubular element 110 ismade of an electrically insulating material e.g. aluminum oxide. Thisprevents the electrodes (between which a liquid connection isestablished) from becoming electrically connected (i.e. becomingelectrical equipotential surfaces). Such electrical connection wouldcounteract the initial purpose of having distinct electrodes. Inalternative embodiments, the intermediate tubular elements may compriseportions made of electrically conducting material and coupling portionsmade of electrically insulating material (see e.g. FIG. 14).

In the embodiment shown in FIG. 3, the cooling conduits 105 in thecollimator electrodes 71-80 are connected in series, to convey thecooling liquid sequentially through subsequent collimator electrodes71-80. The supply conduit opening 103 of the last collimator electrode80 is connected to a cooling liquid supply tube 117, for conveying thecooling liquid into the collimator stack 70. The discharge conduitopening 104 of the first collimator electrode 71 is connected to acooling liquid discharge tube 118, for conveying the cooling liquid outof collimator stack 70. A cooling liquid pump 116 (with a heatextraction means) is provided on an outside of the beam generatorchamber 51. The supply tube 117 and discharge tube 118 penetrate thebeam generator chamber 51 at a predetermined location and in anair-tight manner. On the outside of the beam generator chamber 51, thesupply tube 117 and discharge tube 118 are coupled with supply anddischarge ports (not indicated) of the cooling liquid pump 116. On theinner side of the beam generator chamber 51, the supply tube 117 and thedischarge tube 118 are provided with further bellow structures 119 fordamping motional fluctuations, so as to prevent transient forces andmechanical resonances from the outer side to be conveyed via the supplyand discharge tubes 117, 118 to the collimator stack 70. Preferably, thefurther bellow structures 119 are shorter than a tube diameter, toeffectively attenuate vibrations.

According to the shown embodiment, the cooling liquid is preferablyinitially pumped into the collimator stack 70 at the downstream region(i.e. supplied to the last electrode 80), and the heated cooling liquidis pumped out of the collimator stack 70 at the upstream region (i.e.discharged from the first electrode 71). This arrangement produces a netflow of the cooling liquid along the negative axial direction −Z. Inmany applications, collimator electrodes located downstream of theelectrode stack 70 are subject to more collisions and absorption ofbackscattered and/or secondary electrons, which results in a higher heatload. Initial supply of the cooling liquid to the downstream electrodes,and subsequently conveying the (warmed up) cooling liquid to the moreupward electrodes, is preferred here to provide a more efficient heatexchange between the heated electrodes and the cooling liquid.

Also shown in FIG. 3 is that the intermediate tubular element 110comprises a first substantially straight portion 111 radially facingaway from the first opening 103, a second substantially straight portion112 radially facing away from the second opening 104, and asubstantially curved portion 113 connecting the first straight portion111 with the second straight portion 112. An intermediate tubularelement 110 comprising these straight portions 111, 112 and curvedportion 113 in between reduces the risk of buckling, and more securelyguarantees continuous transfer of cooling liquid through theintermediate tubular element 110. The intermediate tubular element 110may be provided with at least one bellows structure 114. The bellows 114enables motional compensation for any differential thermal deformationsbetween the collimator electrode and the adjacent collimator electrode.Inhomogeneous heating of these electrodes and the resulting deformationdifferences will not result in exertion of additional stresses betweenthe electrodes via the intermediate tubular element 110. The bellowsstructure 114 also assist in damping/eliminating mechanical vibrationsthat are coupled into the collimator stack 70.

FIG. 8 shows a detailed top view of a beam generator according to anembodiment. This beam generator may comprise the charged particle source52 and collimator stack 70 as discussed herein above.

The charged particle beam generator 50 is accommodated inside a beamgenerator vacuum chamber 51. The charged particle beam generator 50comprises at least one vacuum pump unit 122, 123 provided at a distanceΔR from an outer perimeter of the collimator electrode stack 70. Thevacuum pump unit 122, 123 forms an elongated structure with a pumpingaperture 122 a, 123 a that is directed parallel with the optical axis,and which has an aperture height Hp that spans at least part of thecollimator height.

In the embodiment of FIG. 8, the beam generator chamber 51 is providedwith at least two vacuum pump units 122, 123, for sustaining a lowvacuum inside the generator chamber 51 and the collimator stack 70during operation. The vacuum pump units 122, 123 are provided at radialdistances ΔR from the outer perimeter of the collimator electrode stack70. The number of vacuum pump units may be increased to e.g. three orfour, depending on the expected inflow of gas molecules from theenvironment into the beam generator chamber 51. The vacuum pump units122, 123 sustain the vacuum by removing molecules travelling through thebeam generator chamber 51. The pumping units 122, 123 may for examplecomprise two getter pumps, which remove free moving gas molecules fromthe beam generator chamber 51 via chemical reaction or surfaceadsorption.

Active pumping surfaces 122 a, 123 a of the pumping units 122, 123extend along a substantial portion or preferably along the entire heightHe of collimator stack 70. A positioning of the pumping units 122, 123with respective pumping surfaces 122 a, 123 a extending substantiallyalong the height He of the collimator stack 70 yields a saving of thespace within the beam generator chamber 51. The pumping apertures 122 a,123 a preferably face the outer collimator perimeter (which isdelineated by the outer perimeters 85 of the collimator electrodes71-80).

The collimator electrode stack 70 comprises the three support columns 90with the support portions 86. Each support column 90 (e.g. its supportportions 86) extends over a respective angular range ΔΦ1, ΔΦ2, ΔΦ3 alongthe outer electrode perimeter 85. The pumping apertures 122 a, 123 a ofthe pumping unit 122, 123 each spans an angular pump range ΔΦp that hasno overlap with either of the three angular ranges ΔΦ1, ΔΦ2, ΔΦ3. Theshown configuration provides a good pumping efficiency.

The electrode stack 70 may comprise collimator electrodes 71-80 withcooling conduits 105 provided therein (i.e. “coolable collimatorelectrodes”). In this case, the electrode stack 70 also comprisesintermediate tubular elements 110 for connecting a second opening 104 ofa first collimator electrode with the first opening 103 of an adjacentcollimator electrode. The intermediate tubular elements 110 are providedat the outer electrode perimeters 85, spanning a tube angular range ΔΦt.In addition to the above angular positioning properties for the pumpingunits 122, 123, the angular pump ranges ΔΦp of the pumping apertures 122a, 123 a also have no overlap with the tube angular range ΔΦt.

FIG. 9 shows a perspective view of a beam generator 50′ according toanother embodiment. Features and effects relating to the collimatorelectrode stack 70 described above (in particular with reference toFIGS. 3-8) may also be present in the embodiment of the collimatorelectrode stack 70′ shown in FIGS. 9-13, and will not all be discussedhere again. In the discussion of the beam generator 50′ embodiment inFIGS. 9-13, similar reference numbers are used for similar features, butindicated by a prime to distinguish the embodiments.

The beam generator 50′ in FIG. 9 comprises a collimator electrode stack70′ and a beam source vacuum chamber (or “source chamber”) 53′ enclosinga beam source 52′ for generating a charged particle beam along anoptical axis A′. The optical axis A′ extends along an inner part of thecollimator electrode stack 70′.

The collimator electrode stack 70′ comprises ten collimator electrodes71′-80′, each having an electrode aperture 82′. The electrode apertures82′ are coaxially aligned along the optical axis A′, and configured forelectrically manipulating an electron beam that propagates substantiallyparallel with the axial direction Z′ along the optical axis A′.

The first collimator electrode 71′ is provided at an upstream end of thecollimator stack 70′. The beam source 52′ is fixed further upstream onor near an outer face of the first collimator electrode 71′ (see FIG.11). Each of selected collimator electrodes 71′-74′, 76′-80′ comprisesthree support portions 86′ along an outer electrode perimeter. Thesupport portions 86′ accommodate spacing structures 89′ on one sidefacing the axial direction Z′. The support portions 86′ may furtheraccommodate another spacing structure 89′ on the opposite side facingthe negative axial direction −Z′. The spacing structures 89′ areelectrically insulating and resistant against mechanical compression.The spacing structures 89′ may be formed as cylindrical objects with auniform spacer height and flat end surfaces that support or aresupported by the electrode support portions 86′ of adjacent electrodes71′-74′, 76′-80′.

In the shown embodiment, three such spacing structures 89′ are arrangedbetween each adjacent pair of electrodes. Preferably, three spacingstructures 89′ form a tripod configuration. The spacing structures 89′are located at substantially equal radial distances away from theoptical axis A′, and are mutually spaced at angular distances of about180° degrees about the optical axis A′. The arrangement of spacingstructures 89′ and support columns 90′ is further explained below, withreference to FIG. 13.

The collimator electrode stack 70′ comprises three stack support legs93′. Each support leg is connected to a middle region 75 a′ of thecollimator stack 70′ with respect to the axial direction Z′. The supportlegs 93′ cooperate to support the collimator stack 70′ with respect toan external reference frame, which may be formed by the carrier frame 42of the charged particle lithography system 10 in FIG. 1. The resonanceregularization effects described for the collimator electrode stack ofFIG. 4 are also achievable by the currently described collimatorconfiguration.

The middle region 75 a′ of the collimator stack 70′ is selected tocorrespond to the middle collimator electrode 75′, which in this case isthe fifth collimator electrode 75′ counted downstream, starting from thesource 52′ and proceeding along the axial direction Z′. The middlecollimator electrode 75′ comprises an electrode body formed by amechanically strong triangular slab with three corners 92 b′ and threeintermediate electrode body edges 92 c. Each corner 92 b′ accommodates aspacing structure 89′ on one side towards the axial direction Z′ andanother spacing structure 89′ on the opposite side towards the negativeaxial direction −Z′.

Each stack support leg 93′ is connected to a respective electrode bodyedge 92 c. In the embodiment of FIGS. 9-11, each stack support leg 93′comprises a radially protruding tripod 93 a′-96 c′ that is connected tothe collimator stack 70′ in three distinct regions. The stack supportleg 93′ comprises a leg base 95′ with a support foot 99 for connectingthe support leg 93′ to the external reference frame. The stack supportleg 93′ comprises first and second leg members 93 a′-93 b′ that extendradially inward and in locally opposite angular directions from the legbase 95′ towards the middle stack region 75 a′. The stack support leg93′ comprises two leg joints 94 a′-94 b′ for connecting the first andsecond leg members 93 a′-93 b′ to the middle stack region 75 a′, e.g. toa corresponding electrode body edge 92 c′ of the fifth electrode 75′. Inthis embodiment, the leg joints 94 a′-94 b′ are level with an uppersurface of the electrode body, to conserve the angular symmetry of theelectric field generated by the fifth electrode 75′.

Each stack support leg 93′ may also comprise a third leg member 93 cthat extends from the leg base 95′ towards one of the lowermostelectrodes 79′-80′ in the electrode stack 70′.

The leg members 93 a′-93 c are preferably made of mechanically rigidmaterial. At least an intermediate portion of each leg member 93 a′-93c′ is essentially made of electrically insulating material, toelectrically insulate the supported electrodes from each other as wellas from the leg base 95′. Each of the first and second leg members 93a′-93 b′ comprises a radial deflection portion 96 a′-96 b′, which isconfigured for allowing the corresponding leg joint 94 a′-94 b′ todisplace in the radial direction R′ with respect to the leg base 95′. Inthe embodiment of FIG. 9, the radial deflection portions 96 a′-96 b′comprise beams with a curved I-shaped cross-section, which defines aflexible narrow middle region. Each I-beam is oriented mainly transverseto the (local) radial direction, and allows the I-profile to flex withinthe (local) radial-axial plane while remaining mechanically stiff in the(local) angular direction.

As shown in FIG. 10, the leg base 95′ is connected to the support foot99, which comprises a first support foot portion 99 a and a secondsupport foot portion 99 b. The support foot portions 99 a-99 b formdistinct bodies that are moveably arranged with respect to each other.The support foot portions 99 a-99 b may be interconnected by a resilientmember 100 positioned between the first support foot portion 99 a andthe second support foot portion 99 b. The resilient member 100 permitsthe first and second foot portions 99 a-99 b to mutually displace withina predetermined range. The resilient members 100 may for example beformed by two leaf springs 100 a-100 b that both extend parallel withthe axial direction Z′ and the (local) angular direction Φ′. The twoleaf springs 100 a-100 b are oriented mutually parallel at differentradial distances from the optical axis A′. Each leaf spring facessubstantially towards the radial direction R′ (i.e. has its sheetsurface normal pointing at least partially in the radial direction R′).Each of the leaf springs 100 a-100 b of one support foot 99 separatelyallows resilient flexing along radial-axial directions. The leaf springs100 a-100 b jointly allow the first foot portion 99 a and the secondfoot portion 99 b to elastically flex along the radial direction R′ in aparallelogram fashion. This allows the first foot portion 99 a to retainits orientation during radial flexing with respect to the second footportion 99 b (and the external reference frame). The leaf springs 100a-100 b may for example be constructed of sheet steel.

The described stack support configuration allowed radial displacementsbetween the leg joints 94 a′-94 b′ and the corresponding leg bases 95′of each stack support leg 93′, as well as radial displacements betweenthe first foot portion 99 a and the second foot portion 99 b of eachstack support leg 93′. The cooperating three stack support legs 93′yield a stack support configuration that may conveniently accommodatedifferential radial deformation of the middle electrode 75′ with respectto the leg bases 95′, while keeping the collimator electrode stack 70′aligned along the optical axis A′.

The support foot 99 may comprise one or more adjustment members 99 c forfine-tuning a height of the corresponding support leg 93′. By separatelyvarying the support heights of the three support legs 93′, the totalheight and tilt of the collimator stack 70′ with respect to the externalframe 42 may be accurately adjusted.

The leg base 95′ may also comprise a gasket 98 that cooperates with asurrounding beam generator chamber 51′ in a manner described hereinfurther below.

In the embodiment of FIGS. 9-13, the source vacuum chamber 53′ enclosesthe beam source 52′.

The source vacuum chamber 53′ is formed by chamber walls with across-section defined in the radial-angular plane that has apredominantly triangular shape with three chamfered corners. Theresulting irregular hexagonal cross-sectional shape of the walls of thevacuum source chamber is arranged in such a manner that the threechamfered wall corners are aligned with the three support columns 90′ ofthe underlying collimator stack 70′. The collimator electrode stack 70′and the source vacuum chamber 53′ are not directly mechanicallyconnected. Similarly, the beam source 52′ and the source vacuum chamber53′ are not directly mechanically connected. Instead, the firstcollimator electrode 71′ comprises engagement members for fixing thecharged particle beam source 52′ to the first collimator electrode 71′on an upper side thereof, and source alignment members for orienting theoptical axis A′ of the generated charged particle beam with a centerlineof the electrode apertures 82′.

Each stack support leg 93′ comprises two chamber support members 101 foraligning and supporting the source vacuum chamber 53′. Is thisembodiment, each chamber support member is formed by an elongatedsupport rod 101, which extends from a leg connection 101 a at thecorresponding leg base 95 towards a chamber connection 101 b thatlocally supports the source chamber 53′. At least one narrowing 101 cmay be provided along the support member 101, to accommodate thermaldifferential expansion. The embodiment shown in FIGS. 9-10 comprises sixsuch support rods 100, which extend upwards and radially inwards.

The support configuration shown in FIG. 9 allows the beam source chamber53′ and the collimator electrode stack 70′ to be supported on the sameexternal reference frame 42 via the same support structure 93′-101 c,while avoiding direct mechanical coupling between the beam sourcechamber 53′ and the collimator electrode stack 70′. This supportconfiguration may advantageously reduce effects of pressure-induceddeformations in the beam source chamber 53′ on the alignment of thecollimator stack 70′. Conversely, the support configuration mayadvantageously reduce effects of thermally induced deformations of theelectrode stack 70′ on the geometry of and vacuum conditions inside thesource chamber 53′. Alternatively or in addition, the proposed supportconfiguration mechanically decouples the extra weight and size of thesource chamber 53′ from the collimator electrode stack 70′, therebyreducing or even eliminating the contribution of the source chamber 53′to the mechanical resonance (eigen-)frequencies of the collimatorelectrode stack 70′. The resulting mechanical resonance frequencies forthe collimator stack 70′ thus become higher and more localized infrequency space. The proposed support configuration for decoupling thesource vacuum chamber 53′ and the electrode collimator stack 70′ may beimplemented as a separate improvement, independently from the mechanicaldecoupling solution between the electrode collimator stack 70′ and thebeam generator vacuum chamber 51′, which is discussed directly below.

FIGS. 10-11 show perspective views of the beam generator embodiment 50′including a beam generator vacuum chamber (or “generator chamber”) 51′and vacuum pumping systems. Features and effects relating to the beamgenerator 50 with generator chamber 51 in FIG. 8 may also be present inthe beam generator 50′ with generator chamber 51′ described below, andwill not all be discussed here again. In the discussion of theembodiment in FIGS. 10-11, similar reference numbers are used forsimilar features, but indicated by a prime to distinguish embodiments.

The beam generator vacuum chamber 51′ is only partially shown in FIGS.10-11. In FIG. 10, only a rear chamber portion 51 a and a lower chamberportion 51 b of the beam generator chamber 51′ are depicted. An upperchamber portion and lateral chamber portions form part of the completebeam generator chamber 51′, but are omitted from FIG. 10 to show thecharged particle beam generator 50′ inside the generator chamber 51′.Lateral chamber portions 51 c-51 e of the generator chamber 51′ aredepicted in FIG. 11.

The beam generator vacuum chamber 51′ is provided with vacuum pump units122′-123′ (e.g. getters) for sustaining a low vacuum inside thegenerator chamber 51′ during operation. The vacuum pumps 122′-123′ areattached to a pump support structure 124, and oriented with their bodyaxes substantially parallel with the axial direction Z. The pump supportstructure 124 has curved surface portions that face substantiallytowards the collimator stack 70′ (viewed along the radial direction R).The vacuum pumps 122′-123′ are attached on a surface portion of the pumpsupport structure 124 that faces substantially away from the collimatorstack 70′. The electric shielding by the pump support structure 124 andthe outward direction of the vacuum pumps 122′-123′ help to reduce theperturbing effects of e.g. the polygonal shape of the vacuum pumps122′-123′ on the electric fields created inside the collimator stack70′.

Each support column 90′ of the collimator electrode stack 70′ extendsover a respective angular range ΔΦ1′, ΔΦ2′, ΔΦ3′ along the outerelectrode perimeter. Only the range ΔΦ1′ is shown in FIG. 11. Theconfiguration with clamping members 91 a′-91 b′ inside aligned throughholes in each support column 90′ advantageously reduces a column widthand therefore also the angular range ΔΦ1′, ΔΦ2′, ΔΦ3′ over which eachsupport column 90′ extends. The reduced column width yields a largerwindow for molecules inside the collimator region to travel withoutobstruction towards the vacuum pump units 122′-123, resulting in ahigher pumping efficiency.

Below, a mechanical decoupling mechanism between the collimatorelectrode stack 70′ and the beam generator chamber 51′ is described.

As viewed along the axial direction A′, the stack support legs 93′ ofthe collimator electrode stack 70′ extend radially outward and protrudebeyond an outer perimeter of the collimator electrodes 71′-80′. Alsoviewed along the axial direction A′, the lower vacuum chamber portion 51b of the generator chamber 51′ delineates an outer chamber perimeter 130that extends beyond the outer perimeter of the collimator electrodes71′-80′ (provided that the collimator electrode stack 70′ is positionedinside the generator chamber 51′). At the angular coordinates of thestack support legs 93′, the outer chamber circumference 130 is“inscribed” with respect to the stack support leg bases 95′ (i.e. theouter chamber perimeter 130 locally lies at a smaller radial distancefrom the optical axis A′ than the leg bases 95′ do).

To accommodate the protruding stack support legs 93′, the lower vacuumchamber portion 51 b is provided with three lateral chamber apertures132 in the chamber wall. The chamber apertures 132 are located atangular coordinates that correspond with the respective stack supportlegs 93′. Preferably, each lateral chamber aperture 132 has a shape thatis complementary to a local outer perimeter of a corresponding supportleg 93′. In the embodiment of FIG. 10, each lateral chamber aperture 132has a predominantly rectangular shape to accommodate a corresponding legbase 95′ with a locally rectangular cross-section. The lateral chamberapertures 132 are preferably shaped similar to (i.e. congruent with) thelocal perimeters (cross-sections) of the corresponding support legs 93′,but other aperture shapes are possible, provided that the (localperimeter of the) support leg can be accommodated and that the supportleg is allowed to protrude through the chamber wall while avoidingdirect rigid connection with the wall of the generator chamber 51′.

As described herein above, the stack support members 93′ may eachcomprise a gasket 98 for connecting to the surrounding generator chamber93′. The gasket 98 is arranged and configured to flexibly connect thecorresponding stack support member 93′ to the lower vacuum chamberportion 51 b along the edge of the lateral chamber aperture 132. Inaddition, the gasket 98 is formed to cover and seal a void between thelateral chamber aperture 132 and the support leg 93′. The resultingsealing configuration allows different vacuum conditions to be appliedon both sides of the lateral chamber aperture 132 (i.e. on the insideand outside of the generator chamber 51′). In the embodiment of FIGS.10-11, the gasket 98 of each stack support member 93′ is formed by aflat rectangular washer made of synthetic rubber (more particularly, avacuum-compatible fluoropolymer elastomer like Viton®), which surroundsthe leg base 95′ of the stack support member 93′.

The resulting beam generator configuration allows the accommodation ofthe collimator stack 70′ on the inside of the generator chamber 51′,while enabling the collimator stack 70′ and the generator chamber 51′ tobe independently supported by the external reference frame. Direct rigidmechanical coupling between the collimator stack 70′ and the generatorchamber 51′ is thereby avoided.

The proposed mechanical decoupling between the collimator stack 70′ andthe beam generator chamber 51′ may advantageously reduce the effects ofpressure-induced deformations of the generator source chamber 51′ on thealignment of the collimator stack 70′, and/or reduce effects ofthermally induced deformations of the electrode stack 70′ on thegeometry of the generator chamber 51′.

Alternatively or in addition, the proposed mechanical decoupling mayreduce or even eliminate the contribution of the generator chamber 51′to the mechanical resonance (eigen-)frequencies of the collimatorelectrode stack 70′.

Alternatively or in addition, the proposed beam generator configurationallows the collimator stack 70′ to be operated under vacuum conditionscreated inside the generator chamber 51′, while position and alignmentof the collimator stack 70′ can still be adjusted from outside thevacuum chamber 51′. This greatly facilitates alignment and performancetesting of the collimator stack, and helps to improve beam accuracy.

The proposed support configuration with mechanical decoupling allows theconstruction of a generator chamber 51′ that has relatively thin wallsand low mass. The described beam generator embodiment 50′ can thereforebe conveniently formed as a module that is insertable into and removablefrom a carrier frame 42 provided inside a vacuum chamber 30 of a chargedparticle lithography system 10 (e.g. shown in FIG. 1).

As indicated herein above, either one of the proposed supportconfigurations (i.e. for mechanically decoupling the beam generatorchamber 51′ and the electrode collimator stack 70′ on the one hand, andfor mechanically decoupling the source vacuum chamber 53′ and theelectrode collimator stack 70′ on the other hand) may be implementedalone. The embodiment described with reference to FIGS. 9-10nevertheless illustrates that these decoupling solutions may also beimplemented together, by utilizing the same stack support structure andthereby keeping the required space and constructional complexityrelatively low.

Both of the mechanical decoupling solutions may be considered distinctsolutions, and neither of these solutions requires that the collimatorstack supports 93′-96 b are connected to a middle region 75 a′ of thecollimator stack 70′. The described mechanical decoupling between thebeam generator chamber 51′ and the electrode collimator stack 70′ maygenerally be applied in any beam generator that comprises a vacuumchamber with an electrode stack on an inside, and stack supports thatare attached to a lateral region of the collimator electrode stack.

The embodiment described with reference to FIGS. 9-10 neverthelessillustrates that these decoupling solutions may be implemented togetherwith collimator stack supports 93′-96 b that engage in the middle region75 a′ of the collimator stack 70′, to beneficially lower resonancesensitivity of the collimator electrode stack 70′ to all the threeresonance frequency effects discussed herein above, while utilizing thesame stack support structure and thereby keeping the required space andconstructional complexity relatively low.

FIG. 12 schematically shows that, on a lower (i.e. downstream) side ofthis second embodiment of the beam generator 50′, the collimatorelectrode stack 70′ and the beam generator chamber 51′ are configured toremain mechanically separated. The beam generator chamber 51′ and thecollimator electrode stack 70′ can thus remain separately supported bythe external reference frame 42. FIG. 12 shows that the beam generatorchamber 51′ comprises bottom plate 134, which forms part of the lowerchamber portion 51 b shown in FIG. 10. The bottom plate 134 comprises aradially inner chamber plate portion 134 a that is relatively thin andlocated radially proximate to the collimator electrode stack, and aradially outward chamber plate portion 134 b that is thicker than theradially inner chamber plate portion 134 a, and which is locatedradially closer to the outer chamber perimeter 130. The inner plateportion 134 a is located proximate to the last collimator electrode 80′.In particular, the inner plate portion 134 a is proximate to theradially inner electrode portion 80 a′ in the radial direction R′, andproximate to the radially outer electrode portion 80 b′ in the axialdirection Z′. A narrow gap ΔZ is defined between the inner plate portion134 a and the last collimator electrode 80′. This gap ΔZ preferably hasa constant height along the radial direction R′. Preferably, the heightof the gap ΔZ is approximately 0.5 millimeters or smaller.

Furthermore, the surfaces delineating this gap ΔZ preferably have smoothcurvatures, in particular at a radially inward distal end of the innerplate portion 134 a, to avoid electric discharge between the lastcollimator electrode 80′ (which may be kept at an electric potential inthe order of 1 kilovolt during operation) and the inner plate portion134 a of the beam generator chamber 51′ (which is preferably kept atground potential during operation).

The resulting support configuration allows the beam generator chamber51′ and the collimator electrode stack 70′ to be independently supportedby the external reference frame 42. For example the external referenceframe 42 may support the beam generator chamber 51′ at its bottom plate134, whereas laterally protruding stack support legs 93′ carry thecollimator electrode stack 70′ and are in turn supported outside thebeam generator chamber 51′ by the external reference frame 42.

FIG. 12 also illustrates that the stack support leg 93′ may be connectedto a penultimate collimator electrode 79′, to increase stability. Thestack support leg 93′ comprises a third leg joint 94 c for connectingthe third leg member 93 c′ a body edge of the penultimate electrode 79′.The third leg joint 94 c may for example be fixed to the penultimatecollimator electrode 79′ by means of a threaded connection, or otherknown methods. The third leg member 93 c may comprise a third deflectionportion 96 c that permits the stack support leg 93 to accommodatedifferential thermal deformations between the middle collimatorelectrode 75′ supported by the first and second leg members 93 a′-93 b′on the one hand (see FIG. 9), and the penultimate electrode 79′supported by the third leg member 93 c on the other hand.

FIG. 12 furthermore illustrates that the inter-electrode heights Hd′between the collimator electrodes 78′-80′ may be constant. Inparticular, the inter-electrode height Hd′ between the penultimateelectrode 79′ and the radially inner electrode portion 80 a′ of the lastelectrode 80′ preferably equals the inter-electrode height Hd′ betweenthe two-to-last electrode 78′ and the penultimate electrode 79′.

FIG. 13 illustrates a configuration of the support columns 90′ in thesecond collimator stack 70′ embodiment. The electrode support portions86′ of adjacent collimator electrodes and interposed spacing structures89′ are axially aligned to define the stack support columns 90′, whichare oriented substantially parallel with the axial direction Z′. Threesupport columns 90′ are formed in this embodiment. Each of the electrodesupport portions 86′ and the spacing structures 89′ is provided with athrough hole, which is extends substantially parallel with the axialdirection Z′. The through holes in each support column 90′ are mutuallyaligned to form an integral column through hole. The aligned throughholes of the support column 90′ accommodate a clamping member 91 a′-91d′ for holding the support portions 86′ and intermediate spacingstructures 89′ together. The clamping member comprises e.g. an axialpre-tensioned rod 91 b′ that pulls together the two distal ends 91 a′ ofthe pre-tensioned rod. The two distal rod ends 91 a′ are coupled to thefirst and last (i.e. outer) electrodes 71′, 80′ respectively. Eachpre-tensioned rod 91 b′ is provided with two narrowings 91 c′, toaccommodate differential thermal deformation between the collimatorstack 70′ and the respective pre-tensioned rod 91 b′. In addition, aspring member 91 d may be provided on one or both distal rod ends 91 a′of each pre-tensioned rod 91 b′, to provide an additional compensationmechanism for differential axial thermal deformation between thecollimator stack 70′ and the respective pre-tensioned rod 91 b′. Theclamping members 91 a′, 91 b′ are preferably made of a strong andnon-magnetic material e.g. titanium. Sufficient radial interspacing isprovided between an outer perimeter of each pre-tensioned rod 91 b′ andthe inner perimeters of the through holes in the electrode supportportions 86′ inside which the pre-tensioned rod 91 b′ is accommodated.

In the case of cylindrical through holes and rods, inner diameters Øsuof the through holes in the support portions 86 and inner diameters Øspof the through holes in the spacing structures 89 are both substantiallylarger than an outer diameter Ør of the pre-tensioned rod 91 b′.

The radial interspacing serves to maintain electrical separation betweenthe respective electrodes 71′-80′ on the one hand and each pre-tensionedrod 91 b′ on the other hand, even if the electrodes experience thermalradial deformations during operation of the collimator electrode stack70′. Due to the required through holes inside the electrode supportportions 86′ of this embodiment, a typical diameter of the electrodesupport portion 86′ will be larger than a diameter of an electrodesupport portion 86 in the collimator electrode embodiment shown in FIGS.4-5, for example about 1.5 times larger.

FIG. 14 schematically illustrates a portion of the cooling arrangementin the embodiment of the collimator electrode stack 70′ shown in FIGS.9-11. FIG. 14 shows the second, third, and fourth collimator electrodes72′-74′, which are formed as collimator electrodes that are eachprovided with a cooling conduit 105′ on an inside of the electrode body.Interconnecting conduits (formed as intermediate tubular elements) 110′are provided between first conduit openings 103′ of first electrodes(e.g. the fourth electrode 74′) and second conduit openings 104′ ofsecond electrodes (e.g. the third electrode 73′). In this embodiment,each pair of interconnected electrodes are directly adjacent, and theresulting cascade of electrodes and interconnecting conduits forms aserial cooling arrangement. In this embodiment, each interconnectingconduit 110′ comprises a first straight conduit portion 111′, a curvedconduit portion 113′, and a second straight conduit portion 112′. Inthis embodiment, the conduit portions 111′-113′ are made of amechanically strong and non-magnetic material e.g. titanium. In contrastto the embodiment shown in FIG. 3, there are no conduit bellows providedbetween the conduit portions 111′-113′. Instead, at least one of thestraight conduit portions 111′-112′ of each interconnecting conduit 110′is provided with an insulating tube connector 115. The correspondingconduit portion 111′-112′ is discontinued inside the insulating tubeconnector 115, and terminates at two distal conduit ends. These distalconduit ends are fixed to two opposite ends of the insulating tubeconnector 115 in a liquid tight manner, by means of insulating tubeconnectors 115 a-115 b. The insulating tube connectors 115 a-115 b maybe formed by compression fittings with O-rings. The insulating tubeconnector 115 is made of an electrically insulating material (e.g.aluminum oxide), which provides electrical insulation between theinterconnected conduit portions. The proposed conduit arrangement withinsulating tube connector 115 ensures that electrical discharge betweeninterconnected collimator electrodes is reduced.

Also in contrast to the embodiment shown in FIG. 3, the supply tube 117′and discharge tube 118′ in the second cooling arrangement are notprovided with further conduit bellows. Instead, the supply tube 117′ andthe discharge tube 118′ (shown in FIGS. 9-10) have considerable lengthsand are provided with curved regions for damping mechanical resonancesoriginating from outside the beam generator 50′.

FIG. 15 shows another embodiment of a collimator electrode stack 70″comprising a stack support system 93″ for supporting the collimatorelectrode stack 70″ with respect to an external reference frame (42, notshown), and connected to a lateral region 97 of the collimator electrodestack 70″. The lateral region corresponds to the outward perimeter ofthe collimator stack 70″, which faces predominantly outward along theradial coordinate. In this embodiment, one leg member 93 a″ of the stacksupport leg 93″ engages with a third collimator electrode 73″. A furtherleg member 93 c′″ of the stack support leg 93″ engages with an eighthcollimator electrode 78″. In this embodiment, the heights He of thecollimator electrodes 71″-80″ are substantially equal. In addition, theinter-electrode distances Hd are substantially equal. The thirdcollimator electrode 73″ and the eighth collimator electrode 78″comprise electrode support portions 86″ with electrode support arms thathave sufficient mechanical strength to jointly support the weights ofthe entire collimator electrode stack 70″ with respect to the stacksupport legs 93″. As a result, also the third collimator electrode 73″and the eighth collimator electrode 78″ comprise thermal expansionspaces 88″ for accommodating differential thermal deformation betweenthe electrode bodies 81″ and the support portions 86″, while keeping thesupport column 90″ in a fixed position.

The descriptions above are intended to be illustrative, not limiting. Itwill be apparent to the person skilled in the art that alternative andequivalent embodiments of the invention can be conceived and reduced topractice, without departing from the scope of the claims set out below.

For example, the above descriptions of collimator electrode stackembodiments and charged particle beam generator embodiments suggest thepresence of exactly three electrode stack support columns and threeelectrode stack support legs. Although the number three is preferred forhigh stability and constructional simplicity, configurations with onlytwo columns and/or legs or with more than three columns and/or legs orare also conceivable.

The support legs in a collimator stack may engage with the spacingstructures in the support columns, as an alternative or in addition toengaging the middle collimator electrode, to establish a balancedsuspension with respect to an external reference frame.

The stack support system may be shaped differently from the describedtriangular and tripod leg structures. The stack support systemsdescribed in the above embodiments extended from the electrode stackpredominantly downwards to the external reference frame. In general, theexternal reference frame (e.g. carrier frame 42) may support theelectrode stack in the middle region via support members that may beoriented in any of a downward axial direction Z (compression stressesexerted on support legs 93 in FIG. 4), an upward axial direction −Z(tensile stresses exerted on support members), a radial direction R(bending stresses on support members), balanced opposite angulardirections (D, or combinations thereof. Furthermore, the radialdeflection portions may be formed differently, e.g. having a differentshape, cross-sectional profile, or made from other resilient materials.

FIG. 16 schematically shows a charged particle beam generator of anexemplary embodiment. The beam generator comprises a charged particlesource 1003 for generating a diverging charged particle beam, acollimator system for refracting the charged particle beam, and anaperture array 1006. The collimator system may comprise an Einzel lenscomprising three lenses 1005 a, 1005 b, 1005 c and a further lens 1005d. The aperture array 1006 is arranged for forming a plurality ofcharged particle beamlets from the beam generated by the source 1003.The beam generator may comprise one or more openings of a pumpingsystem. The opening may be connected to a (vacuum) pump. The one or moreopenings may form an integrated part of the pumping system, or the oneor more openings may be connectible to one or more pumps within thepumping system. The one or more openings may be part of one or morepumps 1220, the pumps 1220 being included by the beam generator. Thepumps may be getter pumps or sublimation pumps, such as titaniumsublimation pumps. Hereafter, exemplary embodiments will be discussed inwhich one or more pumps 1220 are included in the beam generator.

One or more lenses within the collimator system, typically lens 1005 band 1005 d, operate at a high voltage, e.g. a voltage that is higherthan 500 eV. Electrode 1005 b, i.e. the center electrode of the Einzellens arrangement, may be used to refract the charged particle beam. Asuitable voltage for this lens may be 15-25 kV, for example about 20 kV.Lenses 1005 a, 1005 e may be kept at 0V. Further lens 1005 d may be usedto correct aberrations, as will be discussed later. Lens 5 d may operateat a much lower voltage, for example about 1 kV.

The presence of high voltages on non-designated components within thesystem is undesired, for example because such voltages create additionalfields that would influence the charged particle beam in an undesirable,and often unpredictable way. Therefore, the lenses 1005 a-1005 d, and inthis embodiment also the aperture array 1006 may be located within ahigh voltage shielding arrangement 1201 for shielding components outsidethe arrangement 1201 from high voltages that are present within theshielding arrangement 1201. Furthermore, the charged particle beam thatis present during use may be shielded from fields originating fromlocations outside the high voltage shielding arrangement 1201, which maynegatively influence the uniformity of the beam and/or may introduceadditional aberrations. Preferably, the shielding arrangement 1201comprises a wire mesh structure. The use of a wire mesh structureinstead of a closed structure with some small openings therein is thatthe volume within the shielding arrangement 1201 can be more easilypumped down to obtain a suitable vacuum pressure.

The one or more pumps 1220 are placed outside the shielding arrangement1201 to avoid that the one or more pumps would be charged. The chargedparticle beam generates heat, in particular as a result of chargedparticles back-scattering from the aperture plate 1006. As a result, theone or more pumps 1220 are heated as well, which could affect theirefficiency. The operation of other components may also be negativelyinfluenced by heating. Therefore, the beam generator may furthercomprise a cooling arrangement 1203 for removing heat, such as heatgenerated within the collimator system. The cooling arrangement 1203 maysurround the high voltage shielding arrangement 1201 and the one or morepumps 1220. As a result, the one or more pumps 1220 may be locatedbetween the high voltage shielding arrangement 1201 and the coolingarrangement 1203. The cooling arrangement 1203 may comprise one or morecooling channels 1204 through which a cooling liquid, such as water, mayflow. The use of active cooling by means of cooling channels with acooling liquid flow therein enhances heat transfer as compared to a heatsink made of a heat conductive material.

Preferably, a magnetic shield arrangement 1205 surrounds the coolingarrangement 1203. The use of a magnetic shield arrangement 1205 blocksexternal magnetic fields which could influence the charged particlebeam. Preferably, the magnetic shield arrangement 1205 comprises one ormore walls comprising a magnetic shielding material with a magneticpermeability greater than about 20,000. Preferably, the magneticshielding material has a magnetic permeability greater than about300,000. Most preferably, the magnetic shielding material also has a lowremanence. Examples of magnetic shielding materials, include, but arenot limited to a type of mu-metal and Nanovate™-EM.

The magnetic shield arrangement 1205 does not block magnetic fieldsgenerated by wiring within the arrangement 1205 to interfere with thecharged particle beam. Such wiring is for example present to charge theelectrodes 1005 b, 1005 d. For this reason, the wires within themagnetic shield arrangement 1205 are preferably straight and oriented ina radial direction with respect to the center of the collimator system.Furthermore, the wiring may be in such a way that the magnetic fields ofdifferent wires cancel each other out as much as possible. Outside themagnetic shield arrangement 1205, the orientation of the wires is ofless importance, because magnetic fields generated by the wires at theselocations may be blocked by the arrangement 1205. Note that the magneticshield arrangement 1205 does not necessarily need to be a closedstructure. In particular at the bottom, the arrangement 1205 may beopen, in FIG. 16 denoted by the dashed line.

All components including high voltage shield arrangement 1201, coolingarrangement 1203 and magnetic field shield arrangement 1205 may beplaced within a vacuum chamber 1101. The use of a separate vacuumchamber for a portion of a lithography apparatus may be useful in amodular design. All components within the vacuum chamber may then forexample be aligned with respect to each other and being tested prior toshipment towards a manufacturing environment.

FIG. 17 schematically shows an overview of an exemplary beam generator.In FIG. 17, preferably the source 1003 is located in an area 1102 with ahigher vacuum than the area 1103 in which the collimator resides. Thecollimator is schematically depicted as a block with reference number1300. The collimator may be supported by a support structure 1230 withfeet 1231. The support structures 1230 may take the form of so-calledA-structures. The support structure 1230 may be connected to a frame1240. To establish a vacuum, the beam generator may comprise one or moreports 1250, 1251 for initial pump-down. Reference number 1260 refers toa flange that may be arranged for coupling in cooling fluid and/orwiring.

FIG. 18 shows an elevated side view of a beam generator 1400 accordingto an exemplary embodiment of the invention. The beam generatorcomprises a housing, which in this embodiment comprises three parts 1401a, 1401 b and 1401 c connected to each other by means of flanges 1402.Housing part 1401 a accommodates a source 1003, housing part 1401 baccommodates an Einzel lens having three electrodes 1005 a, 1005 b and1005 c, and housing part 1401 c accommodates a further electrode 1005 dfor aberration corrections.

At the outside of the housing connections are available foraccommodating supply and removal of cooling fluid to be used by acooling arrangement. A suitable cooling fluid is water. A supply unit,such as a supply tube, for supply of cooling fluid may be connected toan inlet 1405 a of a fluid supply conduit 1407 a. Similarly, a fluidremoval unit, such as a tube, for removal of cooling fluid, may beconnected to an outlet 1405 b of a fluid removal conduit 1407 b.

The housing further accommodates support of a high voltage supply unit1408. The high voltage supply unit 1408 contains a wire 1409 via which ahigh voltage is applied to the middle electrode 1005 b of the Einzellens. Additionally, a high voltage may be applied to the furtherelectrode 1005 d. The wire is suitable insulated by means of ainsulating structure 1410 to avoid discharges.

The beam generator 1400 is placed in a vacuum chamber. The pressure inthe vacuum chamber may be reduced by means of pumps 1411 that areconnected to the housing of the beam generator 1400.

Support structures 1230 and feet 1231 may be used to support the beamgenerator 1400.

FIG. 19 shows a first cross-sectional side view of the beam generator ofFIG. 18. The source 1003 is placed in a separate source chamber 1102.The pressure in the source chamber 1102 may be regulated by means of oneor more pumps 1412. The beam generator comprises multiple pumps 1220that are arranged in circumference of the cavity through which the beampasses during use behind a high voltage shielding arrangement 1201. Thehigh voltage shielding arrangement 1201 in this embodiment comprises awire mesh structure. The use of a wire mesh structure providessufficient shielding from high voltages, while simultaneously allowingthe pumps 1220 to have sufficient access to the space within the highvoltage shielding arrangement 1201 to create a suitable vacuum pressure.

The pumps 1220 effectively regulate the pressure within a chamber formedwithin the housing parts 1401 b and 1401 c.

FIG. 20 shows a second cross-sectional side view of the beam generatorof FIG. 18. In this cross-sectional view, portions of a coolingarrangement of the beam generator are depicted. In particular, FIG. 20shows inlet 1405 a and a portion of a fluid supply conduit 1407 a foraccommodating a supply of cooling fluid, as well as outlet 1405 b and aportion of a fluid removal conduit 1407 b for removal of cooling fluidafter it has absorbed heat in the beam generator.

FIG. 21 shows an elevated side view of the beam generator of FIG. 18. Inthis view, tube splitters 1406 are shown, which divide the streams ofcooling fluid to different portions of the cooling arrangement. In someembodiments, the cooling arrangement is divided in three segments. Anupper segment of the cooling arrangement may then be arranged forcooling the upper electrode 1005 a of the Einzel lens. A middle segmentof the cooling arrangement may then be arranged for cooling the lowerelectrode 1005 c of the Einzel lens. Finally, a lower segment of thecooling arrangement may be used for cooling the further electrode 1005d. It will be understood that in embodiments where a further electrode1005 d is absent, fewer segments may be used.

In the presently shown embodiment, the middle electrode 1005 b of theEinzel lens is not actively cooled by means of a cooling fluid.

FIG. 22 shows another elevated side view of the beam generator of FIG.18. In this view, a patch panel 1420 is shown for arranging a connectionof wiring. Additionally, this view shows the presence of contra weights1430. The contra weights 1430 may be used to adapt the center of mass ofthe beam generator so as to allow a stable structure with morepredictable characteristics.

In some embodiments, such as the embodiment discussed with reference toFIGS. 18-22, a cavity within the collimator lens may form a chamber witha mostly closed nature, i.e. the housing surrounding the collimator lenshas limited openings. As a result, one or more pump outlets, in someembodiments part of pumps 1220, may create a relatively low vacuumpressure within the cavity, e.g. a pressure in the order of 10⁻⁶ bar,but lower pressures up to 10⁻¹⁰ bar are achievable. A low pressurewithin the collimator lens reduces ionization of residual moleculeswhich could not only negatively affect the charged particle beam, butalso may lead to actual impingement of ions onto the source 1003. Suchimpingement could seriously limit the lifetime of the source 1003, andis therefore undesirable.

The various embodiments have been discussed with reference to electronbeam lithography processing. However, the principles discussed hereinabove may equally well be applied to generation of other chargedparticle beam types (e.g. beams of positive or negative ions), and toother types of charged particle beam processing methods (e.g. toelectron beam based target inspection).

The embodiments have been discussed with reference to a collimatorelectrode stack that is adapted for collimating a beam of chargedparticles. Electrode stacks that are generally configured formanipulating the path, shape, and kinetic energy of one or more chargedparticle beams are understood to be also covered.

1-20. (canceled)
 21. An electron-optical module of an electron-opticalapparatus, the electron-optical module comprising: a vacuum chamber; ahigh voltage shielding arrangement located within the vacuum chamber;and an aperture array configured to form a plurality of beamlets from anelectron beam and located within the high voltage shielding arrangement,wherein the electron-optical module is configured to be removable fromthe electron-optical apparatus.
 22. The electron-optical module of claim21, further comprising a magnetic shield arrangement, wherein theaperture array is within the magnetic shield arrangement.
 23. Theelectron-optical module of claim 22, further comprising a coolingarrangement configured to remove heat generated by the electron-opticalmodule, the cooling arrangement being within the magnetic shieldingarrangement.
 24. The electron-optical module of claim 21, furthercomprising a cooling arrangement configured to remove heat generated inthe electron-optical module, the cooling arrangement being around thehigh voltage shielding arrangement.
 25. The electron-optical module ofclaim 24, wherein the cooling arrangement comprises one or more coolingchannels configured for a flow of a cooling liquid.
 26. Theelectron-optical module of claim 21, further comprising a pump.
 27. Theelectron-optical module of claim 26, wherein the pump is outside thehigh voltage shielding arrangement.
 28. The electron-optical module ofclaim 22, further comprising a pump outside the high voltage shieldingarrangement and within the magnetic shielding arrangement.
 29. Theelectron optical module of claim 24, further comprising a pump outsidethe high voltage shielding arrangement and within the coolingarrangement.
 30. An electron-optical apparatus comprising theelectron-optical module of claim 21, wherein the electron-opticalapparatus and the electron-optical module are configured for theelectron-optical module to be removable from the electron opticalapparatus.
 31. The electron-optical apparatus of claim 30, furthercomprising a carrier frame configured to enable removal and insertion ofthe electron-optical module.
 32. The electron-optical module of claim31, further comprising another vacuum chamber, wherein the carrier frameis located within the another vacuum chamber.
 33. The electron-opticalapparatus of claim 30, wherein the electron-optical apparatus is aninspection apparatus.
 34. An electron-optical apparatus comprising anelectron-optical module, wherein the electron-optical apparatus and theelectron-optical module are configured for the electron-optical moduleto be removable from the electron-optical apparatus, theelectron-optical module comprising: a vacuum chamber; a high voltageshielding arrangement located within the vacuum chamber; an aperturearray configured to form a plurality of beamlets from an electron beamand located within the high voltage shielding arrangement; and a coolingarrangement configured to remove heat from the electron-optical moduleand being around the high voltage shielding arrangement.
 35. Theelectron-optical apparatus of claim 34, wherein the electron-opticalmodule further comprises a magnetic shield arrangement comprising one ormore walls, wherein the aperture array is within the magnetic shieldarrangement.
 36. The electron-optical apparatus of claim 34, wherein theelectron-optical module further comprises a pump outside the highvoltage shielding arrangement.
 37. The electron-optical apparatus ofclaim 36, wherein the cooling arrangement is configured to surround thepump and/or the high voltage shielding arrangement.
 38. Theelectron-optical apparatus of claim 36, wherein the pump is configuredto regulate a pressure of a space within the high voltage shieldingarrangement, wherein the pump is outside the high voltage shieldingarrangement.
 39. The electron-optical apparatus of claim 34, wherein theelectron-optical apparatus is configured for inspecting a substrate andthe electron-optical module further comprises: an electron sourceconfigured to generate the electron beam to be projected onto thesubstrate; and another vacuum chamber for accommodating components ofthe electron-optical module, wherein the high voltage shieldingarrangement is configured to shield components outside the high voltageshielding arrangement from high voltages that are present within thehigh shielding arrangement and the aperture array is configured to formthe plurality of beamlets from the electron beam.
 40. Theelectron-optical apparatus of claim 34, wherein the electron-opticalmodule and the electron optical apparatus are configured so that theelectron-optical module is removable from the electron-opticalapparatus.